Rails: Cannot add :precision or :scale options with change_column in a migration?

Question

This seems to have been asked before: rails decimal precision and scale

But when running a change_column migration for :precision or :scale they don't actually affect the schema or database, but db:migrate runs without errors.

My migration file looks like this:

class ChangePrecisionAndScaleOfPaybackPeriodInTags < ActiveRecord::Migration
  def self.up
    change_column :tags, :payback_period, :decimal, { :scale => 3, :precision => 10 }
  end

  def self.down
    change_column :tags, :payback_period, :decimal
  end
end

But my schema (and the data) remains as:

t.decimal  "payback_period"

Anybody else have this issue?

Thanks,

Josh

score 36 · Answer 1 · answered Apr 18 '11 at 02:01

Had a related (but not same) problem. I was just changing scale, so when changing the :scale you need the full line:

change_column :something, :weight, :decimal, :precision => 10, :scale => 2

omitting :decimal (which it already was) and :precision (which already was 10) will cause the migration to fail.

score 6 · Accepted Answer · edited Jun 20 '20 at 09:12

Does Not Work for SQLite3

For this simple test app that I'm running I have SQLite3 setup. Apparently, SQLite3 doesn't rely on column type declarations and is more dynamic, looking at the column's content instead - as was stumbled upon here:

Modify a Column's Type in sqlite3

I haven't tested it but I'm sure that's why the schema wasn't being changed, because change_column doesn't translate to anything in SQLite3.

Thanks for the replies guys.

score 1 · Answer 3 · answered Mar 15 '10 at 21:18

1

Delete and regenerate db\schema.rb file.

rake db:schema:dump

answered Mar 15 '10 at 21:18

Harish Shetty

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No joy, still shows same thing. Plus, using the app shows that the migration options have had no effect. – Joshua Pinter Mar 15 '10 at 21:20
I ran the same script and `schema.rb` file changed accordingly. – Harish Shetty Mar 15 '10 at 22:03
I tried it again and still nothing. Perhaps having to do with content already in the database? – Joshua Pinter Mar 16 '10 at 20:33

score 0 · Answer 4 · answered Mar 16 '10 at 22:00

0

A hack, but it should get you where you need to go:

class ChangePrecisionAndScaleOfPaybackPeriodInTags < ActiveRecord::Migration
  def self.up
    execute "ALTER TABLE tags CHANGE payback_period DECIMAL(3,10)"
  end

  def self.down
    change_column :tags, :payback_period, :decimal
  end
end

answered Mar 16 '10 at 22:00

Benson

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Good suggestion, but this didn't work either. I went rooting around trying to find proper syntax for altering a column type in sqlite3 and found there is no way. I'm sure with mysql or another db, I wouldn't even have a problem. Posting an answer here. – Joshua Pinter Apr 02 '10 at 22:23

Rails: Cannot add :precision or :scale options with change_column in a migration?

4 Answers4

Does Not Work for SQLite3

Linked